What is the placenta? Describe its functions. Explain how parturition is induced.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define in one line. The placenta is the structural and functional unit between the foetus and the mother, formed by chorionic villi interlocking with uterine tissue.
2 · Exchange functions. It supplies oxygen and nutrients, removes carbon dioxide and wastes, and is joined to the embryo by the umbilical cord.
3 · Endocrine function. It makes hCG, hPL, estrogens and progestogens; relaxin comes from the ovary late in pregnancy.
4 · Parturition: the signal. The fully developed foetus and the placenta trigger mild contractions, the foetal ejection reflex.
5 · Parturition: the oxytocin loop. Oxytocin from the maternal pituitary causes stronger contractions, which release more oxytocin, until the baby is pushed out through the birth canal.
6 · Link to daily life. After birth, colostrum gives the baby antibodies, so doctors recommend breastfeeding.
7 · Close in one line. So the placenta sustains the pregnancy, and the oxytocin loop brings it to an end in birth.
Scoring tip: Name hCG, hPL and relaxin as the pregnancy-only hormones. It is a favourite marking point inside the long answer.
